A transmission line is a material medium or structure that forms all or part of a path for directing the transmission of electromagnetic waves or acoustic waves. Typical transmission lines for transmitting high frequency electromagnetic waves include coaxial cables, microstrips, striplines, etc. A coaxial cable confines the electromagnetic wave to the area inside the cable between a center conductor and a shield. The dielectric material inside the cable is the medium for transmission of the wave energy. A microstrip consists of a conducting strip separated from a ground plane by a dielectric layer known as the substrate. A stripline is a strip of conductor surrounded by dielectric material and sandwiched between two parallel ground planes. High frequency electromagnetic waves travel within the transmission lines. An important factor of the transmission line is its characteristic impedance, which is determined by structure and physical dimensions of the transmission line, and physical properties of the dielectric medium, such as resistance, inductance and conductance. Particularly for microstrips and striplines, width of the strip, thickness of the dielectric material and relative permeability of the dielectric material determine the characteristic impedance.
Connecting different types of components or transmission lines having different impedance levels requires a transformer. In high frequency circuit design, transmission line transformers and other distributed components are commonly used. For a single-stage quarter wave transformer, the transformer impedance is the geometric mean between the impedance of a first component (such as a load) and a second component (such as a source):ZT=(ZL*ZS)^0.5
A multi-stage transformer may be formed by piling single-stage quarter-wave transformers in series. Each transformer section has an intermediate impedance. In the multi-stage transformer, the impedance mismatch between any two transformer sections is smaller than that between the component and the single stage transformer.
Characteristic impedance of a homogenous dielectric material for a certain electromagnetic wave frequency can be determined by conventional methods known in the art. In a composite material, which is an engineered material made from two or more constituent materials with significantly different physical or chemical properties and which remain separate and distinct on a macroscopic level within the finished structure, the overall characteristic impedance depends on the contributions of the individual constituent materials or components. For example, if a composite comprises a homogenous matrix and ultra-fine nanoscale particles, the characteristic impedance of the composite may be influenced by the added particles.
Composite materials containing nanoscale particles are known in the art and they have numerous applications. U.S. Pat. No. 4,158,862 discloses a method for producing permanent magnetic recordings. The method comprises the steps of: (a) coating a support (substrate) with a polymerizable magnetic ink which contains ferromagnetic particles in a polymer solution; (b) while the ink is still fluid, subjecting the magnetic ink to a magnetic field to orient the magnetic particles contained in the ink in a predetermined direction; and (c) selectively polymerizing, by irradiation, certain areas of the magnetic ink coating corresponding to parts of the recorded message which are to have the magnetic orientation imposed in step (b). As the result, the cured coating layer contains magnetic particles aligned in a direction that is determined by the external magnetic field.
U.S. Pat. No. 3,791,864 describes fabrication of decorative patterns by melting a surface comprising magnetic particles, applying a magnetic field to produce the pattern, and then allowing the surface to cool, thereby retaining the pattern.
U.S. Pat. No. 6,777,706 discloses an optical device that comprises an optical waveguide. The optical waveguide comprises an organic semiconductive material that includes a substantially uniform dispersion of light transmissive nanoparticles. The presence of the nanoparticles influences the refractive index of the organic layer. The organic material is a polymer material. The nanoparticles may be of a metallic material.
U.S. Pat. No. 7,072,565 also discloses an optical waveguide that is made of nanoparticle composite materials.
What has been used in optical circuits may be similarly applied in simplifying design and manufacturing of transmission lines, transmission line transformers, etc. in radio frequency (RF) and/or microwave circuits. Potentially, very high frequency circuit design may be based on principles of these dielectro-magnetic waveguides.